The invention relates to the field of telecommunications and more particularly to cables serving for establishing long distance connections.
The increasing demand for new telephone lines involves a ceaseless widening of the spectrum of frequencies used for transmission. For example, the frequency band transmitted in analog systems using conventional coaxial cables attains at the present day 60 MHz and new higher frequency analog and digital transmission systems are under study among which mention may be made of the optical transmission systems employing optical fibres. The techniques employed and the associated equipment cover a large scope. Nevertheless, since cable laying is costly and complex, it is cost saving to foresee even at this time the establishment of wide band connections within the optical spectrum. The present invention relates essentially to a coaxial cable of the type currently utilized for long distance liaisons, including the elements necessary for transmission in wide band systems at optical frequencies, without these elements in any way disturbing the characteristics of coaxial transmission or the operations necessary for laying and splicing of the coaxial trunk.
The present invention relates to a long distance transmission cable compatible with present-day equipment, due to electrical transmission of the "conventional" coaxial type, capable furthermore of transmitting a wide band in the optical domain.
The cable according to the invention has the following advantages:
The increase of the bandwith obtained by the optical fibres may be considerable without, however, interfering with the transmission of the coaxial type; thus, it is possible to carry on installation of present-day equipment with a quarantee that the latter will not subsequently be affected; PA1 The external dimensions of the cable, its impedance and its attenuation remain practically unchanged; PA1 The relatively thick external conductor of the present-day coaxial cable protects the optical fibres against stresses of external origin during all the steps of the cable manufacture and also during transport thereof and laying in place thereof. Consequently, the increase in unit attenuation of the fibres subsequent to the cable manufacture is minimal; PA1 Introduction of the optical fibres into the present-day coaxial cable is a supplementary step introduced into a manufacturing process without affecting conventional machines and, consequently, it limits the investment necessary for the manufacture of the novel cable.